In the manufacture of consumer packages for liquid contents such as milk, juice or the like, use is often made of a flexible laminate comprising layers of paper and plastics. In one prior art type of packaging machine, the packaging laminate is supplied in web form. The machine--under continuous advancement of the laminate--progressively reforms the laminate into a tube which is filled with the desired contents, transversely sealed and cut off in the sealing zones for the formation of individual, liquid-tight package containers. In connection with the transverse sealing, forming processing of the packaging material tube also takes place so that its substantially circular cross-sectional configuration is converted into a quadrilateral, preferably rectangular, cross-sectional configuration. This forming process takes place using pairwise cooperating flaps which are U-shaped in cross-section and which are pivotal between an open position and a closed position in which they together surround a portion of the laminate tube and cause the tube to assume the desired quadrilateral cross-sectional configuration. Each packaging machine comprises at least two pairs of flaps which, in addition to the above-mentioned operative movements between open and closed positions, are also reciprocated along the packaging material tube so that they alternatingly surround a portion of the packaging material tube and progressively displace it downwardly.
In the manufacture of package containers using the above method, it has been found that, in certain types of packaging laminates, pinch or clamp deformation occasionally occurs in the packaging material tube. When the flaps are pivoted from the open to the closed position, the tube is pinched between the shanks of the U-shaped flaps, which gives the packaging laminate longitudinal, sharp creases and, on occasions, also causes the plastic layer of the packaging laminate to be damaged so that leakage occurs. Naturally, this is undesirable and may, in addition, in the manufacture of sterile package containers, cause sterility in the interior of the packaging laminate tube to be breached so that a risk of infection to the packed contents arises.
Many attempts have previously been made to obviate the above-outlined problem, for example by coating the inside of the flaps with a low friction material in order that the packaging laminate may more readily slide into the U-shaped recesses of the flaps and is not pinched between the flaps. However, despite this and other attempts to solve this problem, no satisfactory solution has hitherto been presented.